Adaptive relay selection algorithm in decode-and-forward cooperative communication networks

An adaptive relay selection algorithm(ARS) is proposed to optimize the performance of decode-and-forward cooperative communication networks, both system outage probability and average numbers of cooperative relays are analyzed. When the direct transmission between source and destination is fail, according to the channel quality, the destination orders relay nodes in the decode set, and the ordered relays are included in cooperation in turn until the instantaneous received SNR at destination is not smaller than the preset SNR threshold. Simulation results show that, the proposed algorithm can get optimal outage performance, decrease the average numbers of cooperative relays efficiently, to incrense bandwidth efficiency and reduce system overhead.     

An optimal equivalent subchannel algorithm for low voltage power line communication system

According to the low voltage power line channel features,combined with adaptive bit loading and power allocation algorithm,an optimal equivalent subchannel algorithm is proposed.Under the condition of fixed amount of transmitted bits and the minimum transmitted power model,impact of optimal equivalent subchannel on the system performance is studied.The optimization algorithm sorts subchannels with similar transmission features into groups,thus the signaling load can be reduced,and the spectrum can be better used.The simulation results show that system can get lower bit error rate(BER) by adopting optimal equivalent subchannel algorithm.     

Novel channel estimation algorithm for OFDM/TDM over fast fading channels

For the shortage of tracking ability against fast fading channel of the existing pilot structures and channel estimation algorithms in OFDM combined with time division multiplexing (OFDM/TDM) system, an improved channel estimation algorithm is proposed. The channel transfer functions are obtained by estimating the channel properties with two adjacent time domain multiplexing (TDM) pilot sequences, while the channel state information of the OFDM/TDM symbols is obtained with interpolation Combined with frequency domain equalization based on minimum mean square error (MMSE-FDE), the proposed algorithm can significantly compensate the path loss over fast fading channels. Simulation results show that, compared with the existing channel estimation algorithms, the proposed algorithm can achieve better performance, which is not only capable of dealing with slow fading channels, but also has a better tracking ability against fast fading channels with the same data transmission efficiency.     

Adaptive bit allocation algorithm in an orphogonal frequency division multiplexing system of cognitive radio

An orphogonal frequency division multiplexing(OFDM) based cognitive radio architecture was designed to meet the transmission requirements of a cognitive radio system. After finishing the allocation of subtransmission, and keeping BER within the limit that ensures service quality, an adaptive bit allocation method was proposed to allocate the bit and energy of subtransmission dynamically. The total power for launching needed reached its minimum (or SNR per bit reached its maximum). Compared with the fixed bit allocation method, the proposed method is simpler, decreases the system transmission power, and has better BER performance.     

Influence of MUD on the System Capability of CDMA

In CDMA communication system, the relativities between users result in Multiple Access Interference (MAI). With the increase of users, MAI becomes the main jam of broadband CDMA communication system. Multi-User Detection (MUD) is the most important technology of anti-jamming in the broadband CDMA communication system, which can eliminates MAI effectively by using the information of all user signals to detection single. This paper analyze the expression of system capability without MUD and with MUD, and puts forward the way to increase system capability by using MUD. Then the influence of MUD on CDMA system capability is discussed by MATLAB emulation. Basing analysis and emulation, the conclusion is got: the higher the MUD efficiency, the better the improvement of CDMA system capability; under the same MUD efficiency, the lower data rate, the smaller inter-cell interference, the lower the ratio of bit energy to power spectrum, the better the improvement of CDMA system capability.     

Modeling and control of An LCL bi-directional inductive power transfer system

Since there exist high-frequency switching networks and complicated operating modes in bi-directional inductive power transfer (IPT) system, it is easy to result in high harmonics and EMI interference. An LCL filter network is introduced to effectively filter out the unwanted harmonics in track current and reduce EMI interference. Based on a mathematical model of the power transmission established by complex analysis of the AC variables, under the condition of maximum transmission efficiency, the phase angle differences between the primary input voltage and secondary output voltage U·so are ±90° and the energy is respectively transferred in forward or backward direction. Moreover, the power magnitude can be controlled by adjusting the modulus of U·pi and U·so. In addition, to keep the track current constant, different phase-shifting control strategies are designed in the primary and secondary parts. Simulation and experimental results show that these strategies can not only adjust track current to keep constant but also dynamically change the direction and magnitude of power transmission according to the working conditions and actual needs of the system load to improve the system operating efficiency.     

Improved CMI code in passive induction setting system 〖JP〗

Aiming at the low energy transmission efficiency of the passive induction setting system with the existing codes, an improved CMI code is proposed as baseband code by changing the equivalent average time of high level during a code cycle under 2ASK modulation. The properties are analyzed, such as energy transmission efficiency, power spectrum and the error probability in incoherent demodulation in AWGN channel. The code is successfully applied to passive induction setting system, and the decoding method and measured voltage waveform are given. With the code, the energy transfer efficiency is improved by 60% than that of CMI code. It is not only beneficial to energy transmission, but also has the merit of CMI code that the bit timing information is extracted easily, which is fully utilized in incoherent demodulation to solve the sampling moment error accumulation problem resulted from the instability of internal oscillator.     

An Algorithm to Enhance the Performance of Data Service Over CATV Broadband Networks

Emerging CATV networks are evolution to Hybrid Fiber/Coax plants. It is widely believed that the HFC network will play an important role in providing broadband accessing service to subscribers due to it's large excess bandwidth and high penetration to the home. Asymmetry broadband data service is the main service provided in the HFC broadband access networks now. It's performance will determine whether the subscribers be satisfied or not and affect the growth of HFC broadband access networks. The authors outline the mechanism of transmitting data in the upstream channel of the HFC network, and analyze how it affecting the performance of data service. The performance of data service and TCP protocol in HFC network is examined. An optimal scheme of bandwidth allocating algorithm for the upstream channel is proposed to enhance the performance of the data service over these networks.     

Spatio-temporal channel assignment in multi-radio wireless mesh networks

A method of spatio-temporal channel assignment based on graph decomposition was proposed to solve the ripple effect and link failure problem in multi-radio wireless mesh networks. Network topology was decomposed into subgraphs in several time slots to extend channel assignment from spatial domain to time domain. Then, graph coloring algorithm was used to optimize the channel assignment on the basis of the subgraph in each time slot. Each subgraph obtained channel resource dynamically according to the network constraints to improve the channel assignment efficiency. Simulation results show that, compared to static channel assignment scheme, the impact of negative factors, such as the ripple effect and link failure caused by channel switching, are effectively confined with this strategy. The network throughput is increased at least by 30% while satisfying the constraints on the number of radios and the number of network channels.     

Group based DBF MUD in CDMA mobile communication system

For the CDMA wireless cellular communication system, a new methodology is proposed to combine digital beamforming (DBF) with multi user detection (MUD) technology which harnesses the co channel interference mitigation and obtains better performance. The proposed approach assigns all the users within a cell into separated groups according to their direction of arrival (DOA). Then, only one DBF branch is employed for a singular group so that the main lobe is steered to the desired users in the group and nulls are directed to the mobile stations in other group. Furthermore, inter group interference is degraded by MUD following the DBF. The new strategy simplifies the weight vector calculation and solves the unorthogonal channel problem. Additionally, it decreases the bit error rate. The analysis and simulation illustrate the fruits of the new mechanism.     

Multiple Turbo Codes for Satellite Communications

Satellite communication channel has the characteristic of power limited, band abundance, and powerful error correcting ability FEC scheme is needed. For its near Shannon limit error correcting capability, Turbo codes may be suitable for satellite communication systems. The multiple Turbo codes can utilize channel capacity sufficiency and overcome the disadvantages of power limited for satellite communication systems. Force on the needed for satellite communication systems, multiple Turbo codes is adopted and server decoding schemes were proposed with simulation. Simulation results show that, the schemes proposed can get near channel capacity error correcting performance with short code block.     

AN IMPROVED METHOD OF CALCULATION FOE UNSYMMETRICAL OPEN CONDUCTOR STATES IN THREE-PHASE POWER SYSTEMS

In this paper, the superposition and compensation theorems are employed to calculate the electric values under the unsymmetrical open conductor states in the three-phase power systems without modifying the bus admittance or the impedance matrices of the original networks. In cotrast with conventional algorithms, the method proposed here is highly accurate, fast, convenient and flexible. It can be applied to the unsymmetrical open conductor calculations which offered in power systems for its design and operation, to determine the settings of relay and automatic deyices, as well as accident analysis.     

Analysis of a New Distributed-Pump Scheme Applied in District Heating Network

It is helpful for energy efftciency to use distributed pumps instead of valves to regulate hydraulic balance in a district heating system (DHS). A new scheme of distributed pump-system is presented based on performance comparison of hydraulic regime and power saving of single-heat-source dendritic pipeline networks with regulating valves and/or distributed pumps. Supposing that the new scheme was employed in multi-sources looped-pipe network, theoretical analysis and case study were carried out to evaluate off-design performances including hydraulic self-regulation, supply water temperature stability and power-saving potential. The results indicated that the proposed scheme would contribute to minimizing power consumption, retarding water temperature change, and would be convenient to adjust the quality and quantity independently in the looped-pipe heat supply networks.     

A Subchannel Allocation Policy of Multicarrier CDMA

To attain high rate data and high quality of service in wireless communication, a subchannel allocation policy combined with subcarriers and power allocation is proposed. In the proposed system, instead of identical power over the subcarriers in parallel, each user's DS waveform is transmitted over the subchannels that have large fading amplitude among all the subchannels. The powers of the subcarriers with small fading amplitude are allocated to the subcarriers with large ones. It can effectively suppress multiple-access interference while obtaining diversity gains. The allocation policy based on fading amplitudes has the advantages of low computation and good convergence compared with the policy proposed in other papers. Thus, it is suitable for engineering.     

间套作资源集约利用及对产量品质影响研究进展

简要介绍了间套作对世界粮食安全的重要性,并对间套作领域当前主要的研究进展进行了综述与讨论。首先,综述了间套作复合群体在光能利用特性,指出了间套作可通过增强叶片光合性能和提高光的截获率与转化效率显著提高光能利用率。其次,综述了不同间套作复合群体在氮、磷、钾养分及水分利用等方面存在的竞争和互补利用现象,讨论了各种间套作类型资源高效利用的可能机制。最后,综述了间套作对产量和品质的影响。间套作可以使产量提高20%~50%,合理的种植密度和复合群体结构是高产的关键。不同间套作类型对秸秆和籽粒粗蛋白、粗纤维、粗脂肪、粗灰分及无氮浸出物等营养物质含量和产量的影响。通过以上几个方面的讨论,指出了间套作研究在资源集约利用、产量和品质等方面存在的不足和需进一步研究的问题。     

优化服务视角下的农科研究生英语学习用户研究

为更好地培养高等农业人才,提升农科研究生英语水平,实现农科研究生英语学习效益最大化,运用信息服务理论为指导,运用水平测试、问卷调查、访谈等方法,以中国农业科学院研究生院硕士研究生为例,对现有农科研究生英语学习进行用户调查分析。调查显示,农科研究生英语学习中用户需求客观状态表现为入学英语水平整体偏低,个体差异性大;用户需求的表达状态表现为农科研究生对信息资源内容与信息服务形式均有新的要求;用户信息素养亟待提高,农科研究生虽具有一定的自主学习意识,但自主学习能力较为薄弱。农科研究生需求的客观状态、表达状态与信息素养之间的矛盾为优质教学服务的提供形成了较大的挑战,成为农科研究生英语教学改革的推动力。运用信息服务理论指导研究生英语教学可以明确英语学习过程的真正主体与中心,实现学习者需求与信息服务的最大耦合度以及教学效果的最优化。     

Digital modulation mode recognition based on multi-classclassification of support vector machine

To solve the overfitting, underfitting and local minimum existing in neural networks, a digital modulation mode recognition method based on support vector machine (SVM) is proposed. Seven characteristic parameters are extracted from instantaneous amplitude, instantaneous phase, instantaneous frequency, frequency spectrum, and changes in characteristics of the envelope to train support vector machine. Compared with the existing algorithms, using binary tree theory to design multi-class classifier has the features of simple, high-speed, high-precision. The simulation results indicate that the scheme can achieve 97% recognition accuracy when the signal to noise ratio (SNR) is above 15 dB with the AWGN channel.     

Multipath interference cancellation RAKE receiver with nested structure

A multipath interference cancellation RAKE receiver with nested structure is proposed based on successive interference cancellation method. In the proposed method, the present branch and the demodulated branch form a substructure of the RAKE receiver, while the RAKE substructures are nested. The data estimate of the present branch is obtained by the maximum ratio combination of the demodulator output in the corresponding RAKE substructure. The update of the regeneration signal is achieved by replacing the previous branch data with the present branch data estimate . Performance of the new RAKE receiver was analyzed. Theoretical analysis and simulation results show that the new RAKE receiver with simple structure and easy implementations can suppress the multipath interference and improves the BER performance.     

Computer Aided Decision-Making System of Power System Reliability Evaluation Based on Object-oriented

The reliability is an important component part of research fields in power system. This paper presents an application of object oriented programming to develop reliability evaluation system of electric networks. A new approach to reliability evaluation and graph expression is proposed, and a computer aided decision making system of electric network reliability evaluation using Visual C++ 5.0 under Windows95 environment is developed. The system can provide reliability data for power system operation and plan, which is the foundation for operation and decision making. It has the characteristics of better expansibility, convenient usage, user friendly interfaces and so on.     

Remote Test Method of Relay Protection

Considering the limitation of the field test for relay protection in power system, the paper studies and discusses the remote test method of relay protection in power system. It provides the technology requirements, the technology problems and restricted factors to build the protection test and analysis center. It proposes the method of building the protection test and analysis center. Considering the practice for the transmission of test data, the paper introduces the technology requirements of utilizing dispatching automation system data network to transmit the protection test data. Considering the requirements of microcomputer protection devices for remote test method, the paper presents that there are remote test function and synchronization test function in the field microcomputer protection devices.